BootA Boot is the action of loading and initializing the operating system on a computer by either powering up the whole computer (cold boot), by resetting the hardware and loading the operating system again without switching off the computer (warm boot) or restarting only the parts of the system under the control of other software (soft boot).
The commonly used computer expression boot originates from "bootstrap loaders," which were small programs used in the beginning of the computer era. They functioned as a means of loading more complex programs, which could in turn finally load the application or operating system. The computer "pulled itself up by its bootstraps" to a higher operating state.
In modern computers, the "bootstrap" is located in the ROM or EPROM and loads a program from the "boot block," which is a fixed location on a floppy disk or a hard drive. This program then starts the operating system.
A cold boot is starting a computer by switching on the power switch. This is sometimes necessary, especially after a system crash, due to a computer lock-up or freeze caused by incompatible programs. For example, when two programs try to access the same memory block at the same time or when programs are waiting for an event that doesn't occur. This is often the result of a programming error.
A warm boot consists of a reinitializing of hardware and software without powering the computer down. This might be necessary after a change of the system configuration in order for the new arrangement to become effective. For PC users, a warm boot is the restart of the computer after changing the config.sys file. It should be noted that a warm boot is the first choice over a cold boot when the computer starts to behave erratically, because powering the whole system on and off can cause damage to the hardware under certain circumstances, e.g. through power surges or overloaded circuits.
A soft boot is a reinitializing of certain additional hardware equipment under software control, such as a modem or sound card.